Acoustic signaling device



' PER/MA NEN r/ Oct. 24, 1950 OLT TA 2,527,371

ACOUSTIC SIGNALING DEVICE Filed June 26, 1948 POLE ARM.S\7

MAGNET BENIGNO MOLTENI LUIGI GERLETTI MM M AGE/VT- Patented Oct. 24, 1950 UNITED'STATES PATENT OFFICE Benigno Molteni and Luigi Gerletti, Verese, Italy Application June 26, 1948, Serial No. 35,358 In Italy July 2, 1947 2 Claims. 1

This invention relates to an acoustic signalling device especially suitable for vehicles, such as motorcycles and small cars. i

The acoustic signalling device of the present invention provides the transformation of an alternating electromotive force in directly audible acoustic sounds, the acoustic unit being a separate part as distinct from the vibrating unit, this allowing the vibrating unit to be made of small size and light in weight thereby requiring for its operation a small power easily available even on small vehicles and even when the engine operates at idling speed that is when the R. P. lVL's thereof are reduced to a minimum.

The essential feature of the acoustic signalling device of the present invention is to make use of a permanent magnet the field of which combines with the field of an electromagnet excited with alternating current whereby the electromotive force for energizing the electromagnet coils may be lower than usual, thus reducing the power needed.

Further, in the acoustic signalling devices heretofore known, the electromagnetic unit has to vibrate directly the sound-producing diaphragm, therefore requiring a considerabe electromotive force due to the mass of said diaphragm. According to the invention, the armature instead actuates members of reduced mass which transmit the vibration to the diaphragm which has the only purpose to amplify the generated sound.

Other objects and advantages of the present invention will appear more fully hereinafter from the following detailed description of an embodiment of the acoustic signalling device of the present invention, when taken together with the accompanying drawing, wherein:

Fig. 1 is a side elevation of a complete acoustic signalling device or horn, partially in section, according to our invention;

Fig. 2 is an elevation, partially in section, of the horn, this view being at a 90 angle with respect to Fig. 1;

Fig. 3 is a top view, the right half showing the outer housing, whereas the left half shows the horn with the bell-shaped housing omitted? Fig. 4 is a top view similar to the preceding one but taken at two different levels, the left half showing the coils, whereas the right half shows the vibrating unit.

The horn of the invention is enclosed in a housing I closed by a spherical cover 2. Secured to the bottom of the housing is a magnet 6 of a highly magnetic material such as, for instance, Alnico to which are secured by means of a Strip 8 the pole arms '5. Coils 9 are wound around the pole arms. These coils, which are wound in the same direction and are constituted by several layers of enameled copper magnet wire, are connected in series, while the other two ends are connected to the terminals of the available. source of anralternating electromotive force. I

The above described electromagnetic unit also comprises a small armature H] which is also made of a magnetic material and which is secured in the center of the bottom side of a narrow, flat strip ll made of a resilient material, while a striping member I4 is fixed to the upper side and, thus, forms a part of the vibrating unit. The strip H which extends diametrically across housing I is provided at its outer ends with two metal reinforcements l9 abutting two resilient supports 12, these supports being apertured to allow the passage of screws [3. The screws are adjustable from the outside of housing I and serving to resiliently secure the vibrating unit to the housing, making it possible to regulate the position of the vibrating unit relative to the fixed level of pole arms 1.

The sound or acoustic unit which is positioned above the vibrating unit is substantially constituted by two diaphragms 3 and 4 of a generally circular form, secured in their central zone to a metallic spacer l6 that ensures their accurate relative position. The height of said metallic spacer I6 and the shape of the two diaphragms 3 and 4 are so that the diaphragms form an acoustic chamber which is open at its peripherical edge and allows the propagation of an amplified sound generated by said diaphragms. Through spacer it passes a screw it the position of which is screw-threadedly adjustable through an aper- I ture provided in the center of the cover 2. Interposed between the head of the screw and the spacer is a helical spring l1. The lower diaphragm 3 abuts the upper flange portion of housing l and is locked in this position by the cover 2.

The operation of the acoustic horn described above is as follows:

First, the level of the strip II is adjusted relative to that of pole arms 1 by means of the adjusting screws l3. This adjustment is required to make sure that due to the alternating magnetic field generated by coils 9, the pull on the small armature l0 and therefore the vibrations of the vibrating. unit take place at the exact frequency of the electromotive force applied to the device. The vibrating system is thus automatically synchronized even for the frequency changes that may occur. Next, the vertical position of screw I5 is adjusted so that the lower end of said screw be in engagement with striking member [4, which is indirectly secured to the small vibrating armature [0, as soon as the coils 9 are excited by a suitable current. The oscillations of the screw I 5 are transformed in sound-producing vibrations of the diaphragms 3 and 4, which vibrations increase in intensity and volume due to the acoustic chamber formed by said diaphragms.

Since the acoustic chamber has practically a constant capacity, a particular basic tone will be generated which will vary only as a function of the frequency changes in the electromotive forces applied.

As it appears from the foregoing description, the acoustic horn of the invention offers remarkable advantages in respect to similar devices already known. Above all, it may be applied even to motorcycles and small automotives with high efiiciency which is not possible with acoustic signalling devices of other already known types.

Of course, the shape, dimensions and all the construction details of the above described device may vary according to needs without, however departing from the scope of the present invention.

What we claim is:

1. Alternating current acoustic signalling device comprising a rigid housing, an electromagnetic unit including a permanent magnet and an armature, vibrating means and acoustic means, said permanent magnet having two pole arms secured thereto, an electromagnetic coil being wound on each of said pole arms, said vibrating means consisting of a strip of resilient material having fixed thereto adjacent the free ends of said pole arms the armature and on its opposite face a striking member, said strip being resiliently and adjustably secured at its opposite ends to said housing to allow the armature to be controllably positioned relative to said free ends, said acoustic means including resilient diaphragms and a member, said member being in axial alignment with said striking member to be struck by the striking member and to produce vibrations of the diaphragms, the housing being provided with sound holes.

2. In the device according to claim 1, two resilient diaphragms secured to a rigid spacer centrally arranged between the diaphragms, said diaphragms being shaped so as to form an acoustic chamber open at its peripheral edge, said member passing screwthreadedly through the spacer for adjustably positioning the member relative to the striking member, one of the diaphragms being fixed at its outer edge to the housing to hold the diaphragms, spacer and member, all of which form an acoustic unit, in place.

BENIGNO MOLTENI.

LUIGI GERLETTI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,959,470 Haasis May 22, 1934 2,278,406 Serge Mar. 31, 1942 

